(i) Field to which the invention relates
The invention is with respect to a thermal insulation body made up of a highly dispersed insulating material with or without the addition of mineral fiber wool and opacifier, the insulating body having been cured by a binder.
(ii) The prior art
Known heat insulating bodies of this sort are, generally speaking, likely to undergo loss in form after compaction of the insulating material, because the composition of such a thermal insulating body is, more importantly, dependent on the interlocking and joining together of the finely dispersed particles. For normal handling, in the case of which careless working is likely to be the cause of heavy thrust and shearing forces, boards produced on these lines frequently do not have the desired properties and are readily broken.
For stopping breaking of such boards, when the boards are acted upon by heavy forces, a suggestion has been made in the past (see German Pat. No. 1,954,992) to make use of heat insulation boards in the case of which the particles of material or fibers are compacted and housed within a casing, the casing producing a force acting on the full inner face of the flexible casing, which generally has the form of a sack and is made up of a glass fiber-based or quartz fiber-based material. This inner pressure has the effect of acting oppositely to forces acting on the structure from the outside and which are produced by thrust or shearing effects, so that any fracture of the insulating body within the casing is stopped.
In a further earlier suggestion (see German Pat. No. 2,036,124) the highly dispersed insulating material cased within a sack, and forming therewith thermal insulating boards, was so interlocked with the case on compaction under pressure that a sandwiched structure made up of core material and casing was produced. This insulating material was marked by a high flexural or bending strength, this, however, being responsible for breaking of the board if acted upon by high flexural or shearing forces.
A somewhat different suggestion has been made in U.S. Pat. No. 3,055,831, which is with respect to readily-handled thermal insulating boards. These boards are made up of highly dispersed insulating material mixed with mineral fiber wool and opacifier in a very fine form. Addition takes place of a binder, which is mixed in, and then the mass is cured by heat or by a catalytic reaction. The particles of the binder have to be of the same order of size as the particles of the insulating material so that their grain size is under 0.1 micron. For producing such a grain size, the binder is processed in special-purpose mills, as for example vibratory or ball mills, to get to the right grain size and is then worked into the insulating material mixture with the help of a mixing apparatus, something which is, however, hard to undertake, because not only the fine-grain binder, but furthermore particles of insulating material become clumped at once on mixing as secondary agglomerates, this stopping the desired mixing of the binder and the insulating material. The outcome is an uneven distribution in the binder-insulating material mix, something which has its own undesired effects on the mechanical properties of the completed board. Because only certain, limited insulating material compound structures are kept together by the binder-agglomerate, there is a tendency for the product, after curing, to be broken when acted upon by forces so that, in this case as well, the desired properties are only produced to a limited degree.
The prior art thermal insulating board of German Offenlegungsschrift specification No. 2,748,307 is made up in its core of a mixture of pyrogenic silicic acid or silica, opacifiers and certain mineral fibers, the casing of this core being a layer of mineral fibers with fillers and inorganic binder. The relatively coarse grained fillers of the outer layer are cured with water glass as a binder, something responsible for further interlocking and part-dissolving of the silica within the second layer so that there is a further-going, intimate joining up of the two layers. This sort of processing with binder, however, only makes for a limited protection of the core of the thermal insulating board, becase the relatively coarse covering layer, even in the cured condition, is not specially resistant to rubbing and, for this reason, the mechanical strength of the board is not increased to the degree thought likely by the curing step.